IGF-1 is a 70-amino-acid polypeptide hormone having insulin-like and mitogenic growth biological activities. This hormone enhances growth of cells in a variety of tissues including musculoskeletal systems, liver, kidney, intestines, nervous system tissues, heart, and lung.
The wild-type IGF-1 has the following amino acid sequence with three intrachain disulfide bridges wherein the side-chains of residue pairs A6 and A48, A47 and A52, and A18 and A61, each form a disulfide bond (SEQ ID NO:50):
Gly-Pro-Glu-Thr-Leu-Cys-Gly-Ala-Glu-Leu-Val-Asp-Ala-Leu-Gln-Phe-Val-Cys-  1               5                   10                 15 Gly-Asp-Arg-Gly-Phe-Tyr-Phe-Asn-Lys-Pro-Thr-Gly-Tyr-Gly-Ser-Ser-Ser-Arg-      20                  25                 30                   35 Arg-Ala-Pro-Gln-Thr-Gly-Ile-Val-Asp-Glu-Cys-Cys-Phe-Arg-Ser-Cys-Asp-Leu-             40                  45                   50 Arg-Arg-Leu-Glu-Met-Tyr-Cys-Ala-Pro-Leu-Lys-Pro-Ala-Lys-Ser-Ala 55                   60                 65                  70
While IGF-1 is present in a wide variety of body tissues, it is normally found in an inactive form in which it is bound to an IGF binding protein (IGFBP). Six related IGFBPs are known and have been designated IGFBP1-IGFBP6. See, e.g., Holly and Martin, “Insulin-like Growth Factor Binding Proteins: A Review of Methodological Aspects of Their Purification, Analysis and Regulation,” Growth Regul., 4(Suppl 1):20-30 (1994). IGFBPs play an important role in IGF-1 regulation by exerting inhibitory and/or stimulatory effects on IGF-1 action. For example, about 90% of circulating IGF-1 is present in a trimolecular complex containing IGFBP-3 and acid labile submit. The IGF-1 within such complexes is unable to bind to surface receptors, and is therefore biologically inactive. IGF-1 present within the trimolecular complex also has a substantially longer half-life than uncomplexed IGF-1.
Disruption of IGF-1 action may contribute to a number of physiological disorders including neurodegenerative disorders such as motor neuron disease (i.e., amyotrophic lateral sclerosis (ALS)), muscular dystrophy and multiple sclerosis, cartilage disorders such as osteoarthritis, bone diseases such as osteoporosis, inflammatory disorders such as rheumatoid arthritis, ischemic injuries to organs such as to the heart, brain, or liver, and so forth.
As is well known to those skilled in the art, the known and potential uses of IGF-1 are varied and multitudinous. For example, a number of studies report on the use of IGF-1 as a potential therapeutic agent for treatment of neurodegenerative conditions. See, e.g., Kanje et al., Brain Res., 486:396-398 (1989); Hantai et al., J. Neurol. Sci., 129:122-126 (1995); Contreras et al., Pharmac. Exp. Therap., 274:1443-1499 (1995); Di Giulio et al., Society for Neuroscience, 22:1960 (1996); Di Giulio et al., Society for Neuroscience, 23:894 (1997); Hsu et al., Biochem. Mol. Med., 60(2):142-148 (1997); Gorio et al., Neuroscience, 82:1029-1037 (1998). IGF-1 therapy has been indicated in numerous neurological conditions, including ALS, stroke, epilepsy, Parkinson's disease, Alzheimer's disease, acute traumatic injury and other disorders associated with trauma, aging, disease, or injury. See, e.g., U.S. Pat. Nos. 5,093,137; 5,652,214; 5,703,045; International Publication Nos. WO 90/1483 and WO 93/02695.
Use of IGF-1 therapy for a variety of other conditions has been referred to in a number of publications. See, e.g., Schalch et al., “Modern Concepts of Insulin-Like Growth Factors,” ed. Spencer (Elsevier, N.Y.), pp. 705-714 (1991); Clemmons and Underwood, J. Clin. Endocrinol. Metab., 79(1):4-6 (1994); and Langford et al., Eur. J. Clin. Invest., 23(9):503-516 (1993) (referring to, e.g., insulin-resistant states and diabetes); and O'Shea et al., Am. J. Physiol., 264:F917-F922 (1993) (referring to, e.g., reduced renal function). Also see U.S. Pat. No. 7,258,864 (referring to short stature); U.S. Pat. Nos. 5,110,604 and 5,427,778 (referring to, e.g., wound healing); U.S. Pat. No. 5,126,324 (referring to, e.g., cardiac disorders and growth retardation); U.S. Pat. No. 5,368,858 (referring to, e.g., defects or lesions in cartilage); U.S. Pat. Nos. 5,543,441 and 5,550,188 (referring to, e.g., tissue augmentation); U.S. Pat. No. 5,686,425 (referring to, e.g., scar tissue, localized muscular dysfunction, and urinary incontinence); and U.S. Pat. No. 5,656,598 (referring to, e.g., bone growth). Also see International Publication Nos. WO 91/12018 (referring to, e.g., intestinal disorders); WO 92/09301 and WO 92/14480 (referring to, e.g., wound healing); WO 93/08828 (referring to, e.g., neuronal damage associated with ischemia, hypoxia, or neurodegeneration); WO 94/16722 (referring to, e.g., insulin resistance); WO 96/02565A1 (referring to, e.g., IGF/IGFBP complex for promoting bone formation and for regulating bone remodeling); U.S. Patent Application Publication No. 2003/0100505 (referring to, e.g., osteoporosis); and U.S. Patent Application Publication No. 2005/0043240 (referring to obesity).
Although IGF-1 therapy has been used for a number of physiological indications, results have sometimes been unpredictable. Short-term beneficial effects sometimes do not persist (see, e.g., Miller et al., Kidney International, 46:201-207 (1994)) and undesirable side effects can result, particularly from administration of high doses and/or long-term administration (see, e.g., Jabri et al., Diabetes, 43:369-374 (1994); Wilton, Acta Paediatr., 393:137-141 (1992)). Also, high levels of IGF-1 have been reported to increase risk for prostate cancer (Chan et al., Science, 278:563-566 (1998)).
Accordingly, there is a need in the art for better ways to treat conditions responsive to IGF-1 and/or other proteins that bind to insulin-like growth factor binding proteins. The present invention fulfills these needs and further provides other related advantages.